1. Field of the Invention
This invention concerns air quality control in general, and more specifically deals with structure for use on open topped floating roof tanks. Such structure is applied in order to reduce or minimize the leakage of vapors from liquid hydrocarbons stored in such tanks.
2. Description of the Prior Art
Recent studies have shown that the gaps between the floating roof seal and the inner perimeter of the sheel of a storage tank containing hydrocarbon products, are a major source of undesirable emissions. Such gaps exist because of tank settling, wind load on the shell, rivet heads, seal deterioration, and could be accentuated by any tipping of the roof created or caused by wind.
Wind blowing across the top of a floating roof tank creates a negative pressure region on the leeward side of the shell i.e. inside the open top and above the roof. At the same time, a positive pressure region is created on the other side, i.e. above the roof and below the open top of the tank. The resulting pressure differential causes air-flow into and hydrocarbon vapor flow out of the space below the roof. Such hydrocarbon vapors tend to escape into the atmosphere through any gaps which may exist around the perimeter of the roof.
Consequently, it is an object of this invention to minimize the above indicated losses by reducing or eliminating the pressure differential indicated.
While, heretofore there have been structures applied to floating tank roof-type storage tanks, which have been designated as "wind girders", these have not been effective to change the above indicated conditions that create a pressure differential on the floating roof structure. Such wind girders have been shown in prior U.S. Patents, e.g. Numbers 3,106,310 and 3,589,549.